This invention relates generally to spectrometers, and, more particularly, to a novel spectrometer design based on refractive optical relay systems, which is more compact in physical size and superior in spectral imaging quality than previous designs.
A spectrometer is a known device that is commonly used to examine the spectral, or wavelength dependent, content of light. Light emitted or reflected by a given object or scene is imaged by some means onto the entrance of the spectrometer, usually a slit element that transmits a single line image from the object or scene. The spectrometer in turn re-images this light to another location while dispersing this light according to its wavelength in a direction orthogonal to the orientation of the slit element, where it can readily be observed or recorded.
Because every material has a unique spectral signature, the spectrometer has become a very useful scientific tool in a broad range of scientific and industrial applications including, but not limited to, the monitoring of regional and global environmental conditions, the identification of both airborne and terrestrial objects and surveillance applications, the assessment of unknown substances in forensic applications, the precise characterization of color spectra in colorimetry, and even in the assessment of crop health and irrigation scheduling in the farming industry.
Current optically fast spectrometer designs are either too large in size for many applications, including but not limited to, unmanned aircraft, and forensic fieldwork, or their dispersing elements are too complex and costly to fabricate for commercial applications, or they do not provide enough spatial and spectral imaging quality to meet the required system performance, or they cannot provide a combination of these characteristics simultaneously.
For example, consider some applications of hyperspectral imaging in which it is desirable to have a spectrometer that simultaneously possesses a large spectral bandwidth such as the combined visible, near infrared and short-wave infrared bands, a large spatial field so that a large ground area can be covered with a single fly-over, high spatial and spectral resolutions so that small spatial and spectral features can be resolved, negligible spectral and spatial distortions to facilitate recognition algorithms, a fast optical speed, a very small size and mass so that the system can be transported in an unmanned aerial vehicles (UAV) or be man-portable, and is readily manufacturable from low-cost components.
It is therefore an object of this invention to provide a spectrometer design that is compact in physical size.
It is a further object of this invention to provide a spectrometer design that is low in mass.
It is a further object of this invention to provide a spectrometer design that eliminates the need for complex and costly dispersing elements.
It is a further object of this invention to provide a spectrometer design that provides a high degree of spatial and spectral image quality that is relatively free of spatial and spectral image distortions.
It is a further object of this invention to provide a spectrometer design that provides large spatial and spectral fields.
It is a further object of this invention to provide a spectrometer design that operates over multiple bands of wavelength, forming a separate spectral image for each band or a single extended multi-band image.
It is a further object of this invention to provide a spectrometer design that simultaneously provides a dispersed spectral image and a polychromatic image.
It is a further object of this invention to provide a spectrometer design that simultaneously provides separate spectral images for multiple input scenes.
It is a still further object of this invention to provide a spectrometer design that provides a combination of the characteristics described above with superior trade-offs than have been previously attainable.